The present invention relates to a magnetic film for a magnetic head, more precisely relates to a magnetic film for a write-head of a magnetic head, especially a perpendicular recording head, which is capable of intensifying a writing magnetic field, improving magnetic response and raising recording density.
Conventionally, many elements have been used for multilayered magnetic films so as to achieve many purposes. For example, a giant magnetic resistance was found in a Fe/Cr multilayered film, so that a spin valve film for a read-head was invented (see Phys. Rev. Lett., vol. 62, p. 2472 (1988)). A Co/Pd multilayered film has greater perpendicular magnetic anisotropy than a CoCr alloy film, so it will be used for recording media (see J. Appl. Phys., vol. 87, p. 6887 (1988)). Layer stacking separations of the conventional multilayered films are several nm, and each of the layers is very thin and constituted by several atomic layers.
On the other hand, a NiFe single layer film, whose saturation magnetic flux density (Bs) is 1-1.5T, has been used as a conventional material of a write-head. Thickness of the film is several μm, namely the film is a thick one. In the future, a data transfer rate of a magnetic disk drive unit will be accelerated. Eddy current loss occurs in the thick magnetic film, so that writing performance of the write-head is made worse. To solve the problem, a multilayered film, in which magnetic layers and insulating layers are alternately piled, has been studied. In the multilayered film, resistance of the insulating layers and the magnetic layers is high, and the thickness of the film is less than skin depth, e.g., submicron, so that eddy current loss can be restricted.
To make magnetic anisotropy small and gain enough soft magnetism, amorphous, micro crystals and granular magnetic films have been studied as the magnetic layer. Furrther, by employing the multilayered structure, the magnetic layers are statically magnetic-connected, so that a magnetic circuit is closed and frequency response can be improved. According to J.Magn. Soc. Jpn. vol. 14, p. 379 (1990) and J.Magn. Soc. Jpn. vol. 15, p. 391 (1991), an amorphous metal CoNbZr and a micro crystal FeSiN are used as materials of the magnetic layers. Saturation magnetic flux density of the magnetic layers is 0.8-1.85T. However, recording density will be even higher, so a track width and a pole length of a front end section of a magnetic pole must be smaller so as to write smaller bits.
Further, coercivity of recording media will be increased so as to limit thermal decay of magnetization of magnetic minute particles. Magnetic materials must have high saturation magnetic flux density (Bs) to generate a higher magnetic field for writing data. Therefore, enough magnetic fields cannot be generated with amorphous and microcrystal materials, whose Bs is 0.8-1.85T. An FeCo alloy is a thermal equilibrium alloy having maximum Bs of 2.45T, but its magnetostriction constant (λ) is large, e.g., 30-70×10−6, so an inverse magnetostrictive effect, which is caused by isotropic stress generated while a layer is formed, cannot be ignored. Therefore, it is very difficult for the FeCo single layer to have soft magnetism with uniaxial magnetic anisotropy. In the case of using a magnetic material having isotropic magnetic characteristics as magnetic poles, data recorded on a recording media are apt to be erased by a leaked magnetic field corresponding to a residual magnetization (Br).
Erasing data by a write-head is more remarkable in a single pole type head for perpendicular magnetic recording than a ring head for longitudinal recording. Further, a front end of the single pole type head is formed like a needle. Even if a magnetic material in a state of as-depositing has uniaxial magnetic anisotropy and its Br in a direction of the hard axis is reduced, a leaked magnetic field is generated by shape magnetic anisotropy caused by the shape of the magnetic pole, so that there is possibility of erasing data by the leaked magnetic field. To solve the problem, a magnetic material, which has high Bs and which is capable of restraining uniaxial magnetic anisotropy and shape magnetic anisotropy, is required.
To increase Bs, adding impurities, which accelerate crystal growth, must be restrained. In crystal magnetic materials, e.g., FeCo, columnar growth and enlarging crystals in a thickness direction of a layer are more remarkable than those in amorphous and glanular alloy films. Therefore, roughness of a surface of a layer or unevenness of crystals obstruct to form multilayer with other materials. Namely, materials must be selected with fully considering the roughness.
In the FeCo single layer, a underlayer is formed immediately under the FeCo alloy layer so as to have soft magnetism with high Bs. According to IEEE. Trans. Magn. vol. 36 p. 2506-2508 (2000), an FeCoN magnetic layer has soft magnetism and high Bs, e.g., 2.4T. However, it is difficult to control magnetic anisotropy of the FeCoN single layer. To solve this problem, the FeCoN layer is formed on a underlayer, which is made of permalloy of Ni80Fe20, or the FeCoN layer is sandwiched between the layers made of the permalloy of Ni80Fe20, so that the soft magnetism is improved. In said report, thickness of the FeCoN layer is 0.1 μm, and there is no description about soft magnetism of the layer whose thickness is more than 0.1 μm. To enhance the writing magnetic field, it is effective to make thickness of a high Bs layer of a front end of a magnetic pole 0.1 μm or more. By forming the FeCoN layer on the NiFe underlayer, the soft magnetism is improved by magnetic coupling between the two layers. And, magnetoelastic anisotropy, which is caused by residual stress generated while a layer is formed, is not dominant.
On the other hand, in IEEE. Trans. Magn. vol.38 p. 2225-2227 (2002), a underlayer made of a nonmagnetic material (NiFeCr) is disclosed. The underlayer is capable of improving the soft magnetism of FeCo as well as the underlayer made of NiFe. The fact means that the magnetic coupling between the underlayer and the FeCoN layer is not an essential factor of improving the soft magnetism. The magnetic layer having high Bs and soft magnetism is required so as to write data in a recording media, which has a high coercivity and high recording density, with high writing accuracy and improve magnetic response. However, FeCo layers, which have such required properties, have not developed.